1. Field of the Invention
The present invention relates to a detecting method for detecting internal information of a rechargeable battery to be inspected (this rechargeable battery will be hereinafter referred to as xe2x80x9cinspective rechargeable batteryxe2x80x9d) and a detecting apparatus for detecting internal information of an inspective rechargeable battery. The present invention also relates to an apparatus in which said detecting method is applied and an apparatus including said detecting apparatus. The present invention includes a storage medium in which a software of said detecting method is stored.
The internal information to be detected in the present invention includes the presence or absence of short circuit, electricity storable capacity, remaining capacity (=presently stored electricity quantity=dischargeable capacity), usable capacity (=presently residual electricity quantity which is still able to operate an instrument), internal resistance, and the like, of an inspective rechargeable battery.
2. Related Background Art
In recent years, along with development of semiconductor elements and development of miniature, light-weight and high performance rechargeable batteries, mobile instruments such as portable personal computers, video cameras, digital cameras, cellular phones, and personal digital assistants including palmtop PCs have been rapidly progressed.
Separately, in recent years, the global warming of the earth because of the so-called greenhouse effect to an increase in the content of CO2 gas in the air has been predicted. For instance, in thermal electric power plants, thermal energy obtained by burning a fossil fuel is converted into electric energy, and along with burning of such fossil fuel, a large amount of CO2 gas is exhausted in the air. Accordingly, in order to suppress this situation, there is a tendency of prohibiting to newly establish a thermal electric power plant. Under these circumstances, so-called load leveling practice has been proposed in order to effectively utilize electric powers generated by power generators in thermal electric power plants or the like, wherein using a load conditioner having a rechargeable battery installed therein, a surplus power unused in the night is stored in rechargeable batteries installed at general houses and the power thus stored is used in the daytime when the demand for power is increased, whereby the power consumption is leveled.
Separately, in recent years, electric vehicles comprising a rechargeable battery and which do not exhaust any polluting substances have been proposed. Besides hybrid powered automobiles in which a combination of a rechargeable battery and an internal combustion engine or a fuel cell is used and the fuel efficiency is heightened while restraining exhaustion of polluting substances have been also proposed. As the rechargeable battery used in these electric vehicles and hybrid powered automobiles, a high performance rechargeable battery having a high energy density is expected to be developed.
Such rechargeable battery presently used in the mobile instrument, the load conditioner used for practicing the load leveling, the electric vehicle and the hybrid powered automobile includes typically rechargeable lithium batteries (lithium ion rechargeable batteries) in which reduction-oxidation reaction of lithium is used.
Incidentally, in the mobile instrument, the load conditioner in the load leveling, the electric vehicle and the hybrid powered automobile in which such rechargeable battery as above mentioned is used, it is possible to extend the operation time to the maximum by properly controlling the power outputted from the rechargeable battery depending on internal information of the battery on the side of the apparatus in which the battery is accommodated, or it is possible to avoid occurrence of sudden stall of the operation by previously knowing the time necessary to exchange the battery by way of acquisition of information of the lifetime of the battery in advance.
Particularly, in order to prevent the operation of the mobile instrument, the load conditioner, the electric vehicle or the hybrid powered automobile from being suddenly stopped, it is very important to be able to precisely detecting internal information of the rechargeable battery used therein, represented by electricity storable capacity, remaining capacity (=presently stored electricity quantity=dischargeable capacity), usable capacity (=presently residual electricity quantity which is still able to operate an instrument), and internal resistance of the battery.
In order to detect the remaining capacity of a rechargeable battery, there is known a method wherein the voltage of the battery is measured and based on the measured battery voltage, the usable capacity is estimated.
The term xe2x80x9cremaining capacityxe2x80x9d of the rechargeable battery means a presently stored electricity quantity of the battery which can be discharged. The term xe2x80x9cusable capacityxe2x80x9d means a presently available electricity quantity of the rechargeable battery with which an instrument (or an apparatus) having said rechargeable battery can be still operated. The usable capacity is included in the term remaining capacity.
Aforesaid method is applicable in the case of a lithium ion rechargeable battery whose anode material comprising a non-graphitizing carbon material which is distinguished from a graphite, where because the battery voltage is gradually decreased in proportion to the quantity of the electricity to be discharged, and therefore, the usable capacity of the rechargeable battery can be estimated by measuring the battery voltage. However, it is difficult to precisely detect the remaining capacity of the rechargeable battery by using this method because the battery voltage differs depending on an electric current flown even when the remaining capacity is identical. Besides, in the case where the performance of the rechargeable battery has been deteriorated to close its lifetime, it is extremely difficult to precisely detect the remaining capacity.
Separately, in the case of a lithium ion rechargeable battery whose anode material comprising a graphite series carbonous material, because the battery voltage with respect to the quantity of the electricity to be discharged is flat, it is difficult to estimate the remaining capacity from the battery voltage in accordance with aforesaid method.
There is also known a method in order to detect the remaining capacity of a rechargeable battery, wherein an accumulation discharged-electricity quantity is memorized and the accumulation discharged-electricity quantity is subtracted from a charged-electricity quantity to obtain a remaining capacity thereof. However, this method has such disadvantages as will be described in the following. That is, the current value and the discharge time are necessary to be always memorized. Besides, in the case where the discharge depth of the rechargeable battery is unknown with respect to the discharge depth and additional charging is performed for this rechargeable battery, although the charged-electricity quantity at that time can be detected, the remaining capacity of the rechargeable battery after the rechargeable battery is subjected to charging cannot be precisely detected because the remaining capacity of the rechargeable battery before the additional charging is unknown. When aforesaid method is adopted in this case, because the method is of a way to calculate a remaining capacity by subtracting the total discharged-electricity quantity from the accumulation charged-electricity quantity prior to the discharging, a large error is likely to occur in the measurement.
Therefore, the method is difficult to cope with a rechargeable battery whose performance has been deteriorated to close its lifetime, where it is difficult to precisely detect the remaining capacity.
Now, Japanese Laid-open Patent Publication No. Hei.4(1992)-2066 (hereinafter referred to as document 1) discloses a method for distinguishing the capacity of a lead battery in accordance with recovery characteristic of the battery voltage after pulse discharge.
Japanese Laid-open Patent Publication No. Hei.4(1992)-136774 (hereinafter referred to as document 2) discloses a method wherein for a rechargeable battery, when the power source is ON, discharging is temporarily performed at a large current to detect a decrease in the battery voltage, the detected decrease value is compared with a prejudged battery voltage value, where when the difference is great, the residual capacity is judged to be insufficient.
Japanese Laid-open Patent Publication No. Hei.11(1999)-16607 (hereinafter referred to as document 3) discloses a method wherein for a rechargeable battery, the battery voltage when a prescribed current is applied for a prescribed period of time is measured and the measured battery voltage is collated with a previously established battery voltage-residual capacity corresponding table to estimate a residual capacity of the battery.
However, for a rechargeable battery whose performance has been deteriorated to increase the internal resistance or to decrease the electricity storable capacity, any of the methods disclosed in documents 1 to 3 is difficult to precisely detect the remaining capacity of the battery.
Separately, Japanese Laid-open Patent Publication No. Hei.9(1997)-134742 (hereinafter referred to as document 4) discloses a method wherein for a rechargeable battery, the internal impedance directly before reaching the discharge termination voltage is measured by an impedance-measuring instrument while flowing an alternate current to determine whether or not the rechargeable battery is deteriorated with respect its performance.
However, the method disclosed in document 4 is not practically applicable for the reason that such impedance-measuring instrument for measuring the impedance is required to have an alternate current-generating circuit and because of this, the apparatus involved unavoidably becomes large-sized, and in addition, during when the rechargeable battery is operated, the measurement cannot be performed.
Further, Japanese Laid-open Patent Publication No. Hei.11(1999)-271408 (hereinafter referred to as document 5) discloses a method to detect a degraded battery wherein a rechargeable battery (a lithium ion rechargeable battery) is charged by a constant current-constant voltage with a taper charge (CCCV) regime (this will be hereinafter referred to as xe2x80x9cconstant current-constant voltage charging regimexe2x80x9d or xe2x80x9cCCCV charging regimexe2x80x9d) [wherein charging is commenced at a constant current value and after the battery voltage reaches a given voltage value, the charging is performed at a constant voltage until the termination thereof]. This method is of a way to estimate a deterioration magnitude of the battery from the charged electricity quantity at a constant current, a current drop immediately after the constant current charging is switched to the constant voltage charging, and a current drop rate at the constant voltage charging.
However, the method disclosed in document 5 yet has not reached such a stage that internal information relating to the remaining capacity of the rechargeable battery can be always stably obtained from the charged electricity quantity at the time of the constant current charging and the current drop or the current change rate at the constant voltage charging. Separately, document 5 describes that the remaining capacity when the battery is deteriorated, the charged electricity quantity at the time of the constant current charging, the current drop rate at the time of the constant voltage charging, and the current change drop at the constant voltage charging are correlated. However document 5 does not mention even a suggestion that which factors are the most correlated, what is a reliable method in order to detect the remaining capacity, and specifically, how the remaining capacity is detected. Further, in accordance with the description of Document 5, it is impossible to distinguish whether or not the remaining capacity is decreased when the battery is short-circuited, whether or not the remaining capacity is decreased when the battery is deteriorated to increase the internal resistance, or whether or not the remaining capacity itself is decreased, and therefore, it is impossible to grasp details of a deteriorated state of the battery. Information of whether or not the battery is short-circuited is important not only in order to more safely use the battery but also in order to accurately grasp internal information of the battery.
Incidentally, for a rechargeable battery, when the charge-and-discharge operation is repeated, there is a tendency in that the internal resistance is increased to decrease the charge capacity due to a cause that the electrode active material is deteriorated, the electrode active material is peeled or missed from the collector, or the electrolyte solution is decomposed. Besides, when the connection portions of the leads connecting to the output terminals extending from the battery should be peeled due to a certain case such as vibration or the like, there will be an occasion in that the internal resistance of the battery is increased. In addition, there will be an occasion in that due to a metal deposition or the like by way of electrochemical reaction, a short-circuited portion is occurred between the anode and the cathode and as a result, the internal resistance is decreased while the remaining capacity is decreased.
For such rechargeable battery in which the internal resistance is increased, the remaining capacity is decreased or which is short-circuited, in the case where internal information thereof is intended to detect by the conventional method, it is difficult to avoid occurrence of a large error in terms of the accuracy.
In this respect, there is an increased demand for providing a detecting method and a detecting apparatus which enable one to precisely detect an usable capacity (that is, a presently residual electricity quantity which is still able to operate an instrument) of any of various rechargeable batteries even when they are such that their remaining capacity is decreased or their internal resistance is increased and their performance is deteriorated. Besides, a detecting method and a detecting apparatus which are applicable in any rechargeable batteries in order to precisely detect their lifetime, i.e., deterioration of their performance are expected to be developed.
The present invention is aimed at solving the shortcomings in the prior art in that in any of the proposed methods for detecting internal information of a rechargeable battery, represented by the electricity storable capacity and the like, is inferior in terms of the detection accuracy.
Another object of the present invention is to provide a detecting method and a detecting apparatus which enable one to detect internal information of any rechargeable battery at a high precision even when the rechargeable battery is a rechargeable battery whose performance is deteriorated.
A further object of the present invention is to provide an instrument in which said detecting method or said detecting apparatus is applied.
A still further object of the present invention is to provide a storage medium in which a software program of said detecting method is stored.
A typical embodiment of the detecting method of the present invention is a detecting method for detecting internal information of a rechargeable battery to be inspected (this rechargeable battery will be hereinafter referred to as inspective rechargeable battery) when said inspective rechargeable battery is charged by a constant current-constant voltage charging regime in that charging is commenced at a constant current value I0 and after the battery voltage reaches a given voltage value Vmax, the charging is performed at a constant voltage Vmax until the termination thereof, said detecting method is characterized by comprising at least a step (A) of measuring an elapse of time (t) from the time when a constant current charging mode at a constant current value I0 is shifted to a constant voltage charging mode at a constant voltage Vmax and measuring a charge current value I in the constant voltage charging mode, a step (B) of obtaining a period of time from said shift time to the constant voltage charging until the time when said charge current value I in the constant voltage charging mode reaches a given current value IM, and a step (C) of obtaining a charged electricity quantity of the inspective rechargeable battery in the constant voltage charging mode.
The detecting method may include a step (D) of referring to charge current characteristics of a corresponding normal rechargeable battery as a reference standard of the inspective rechargeable battery in the constant voltage charging mode when said normal rechargeable battery is charged by the constant current-constant voltage charging regime.
The internal information of the inspective rechargeable battery which is acquired by the detecting method of the present invention includes facts about. According to the detecting method of the present invention, even when the inspective rechargeable battery is a rechargeable battery whose discharge depth before the commencement of charging is unknown, to be more specific, even when additional charging is performed for an inspective rechargeable battery in which a certain quantity of electricity is still remained, internal information thereof represented by the remaining capacity can be acquired.
A typical embodiment of the detecting apparatus of the present invention is a detecting apparatus for detecting internal information of an inspective rechargeable battery when said inspective rechargeable battery is charged by a constant current-constant voltage charging regime in that charging is commenced at a constant current value I0 and after the battery voltage reaches a given voltage value Vmax, the charging is performed at a constant voltage Vmax until the termination thereof, said detecting apparatus having at least a means for measuring a charge current value I when the inspective rechargeable battery is charged by the constant current-constant voltage charging regime; a means for measuring an elapse of time (t) from the time when a constant current charging mode at a constant current value I0 is shifted to a constant voltage charging mode at a constant voltage Vmax; a means for measuring a time (tMxe2x80x2) when the charge current value in said constant voltage charging mode becomes to be a given current value IM; a means for measuring a charged electricity quantity Qvcxe2x80x2 in said constant voltage charging mode; a memory means in which an electricity storable capacity (or a nominal capacity) CN of a corresponding normal rechargeable battery and internal information of said normal rechargeable battery when said normal rechargeable battery is charged by the constant current-constant voltage charging regime are memorized, said internal information including the time (tM) when the charge current value in the constant voltage charging mode becomes to be a given current value IM and the charged electricity quantity QCV in the constant voltage charging mode; and an arithmetic means for computing an electricity storable capacity (CNxe2x80x2) of the inspective rechargeable battery from said CN, tM and QVC of the normal rechargeable battery which are memorized in said memory means and said tMxe2x80x2 and QVCxe2x80x2 detected from the inspective rechargeable battery.